The “most important and alarming facet” of Senator Richard Lugar’s primary defeat this week, according to Jonathan Chait, was that conservative Hoosiers punished him for voting to confirm Sonia Sotomayor and Elena Kagan to the Supreme Court. Those votes by Lugar were merely expressions of a “social norm,” the “longstanding practice of extending presidents wide ideological latitude on their Supreme Court picks.”

Lugar’s loss, according to Chait, means that Republican incumbents, fearful of not remaining incumbents, are likely to repudiate this norm, thereby seizing “one of the few remaining weapons the Republican Party has left lying on the ground.” Such escalation could make it impossible for President Obama “to seat any recognizably Democratic jurist” on the Supreme Court, after which it may “become commonplace for the Court to have several vacancies owing to gridlock,” bringing on “a future systemic crisis.”

Chait sees a dramatic asymmetry in the partisan responsibility for the decline of the old, useful spirit of give and take. “The main affliction of American politics is . . . the collision of an increasingly radical Republican Party with a creaky political system poorly equipped to handle unified, fanatical parties.”

There’s a clear problem with this indictment, however. #more#Four of the past five Supreme Court nominees submitted by Republican presidents have failed to receive a majority of Democratic senators’ confirmation votes: Robert Bork (52 against, 2 in favor), Clarence Thomas (46 against, 11 for), John Roberts (22 against, 22 in favor), and Samuel Alito (40 against, 4 in favor). A majority of Senate Democrats, including Hillary Clinton, John Kerry, Barack Obama, and Harry Reid, went further, voting in favor of a filibuster to block Alito’s nomination.

Chait recognizes but does not admit this problem. Under the old, deferential social norm, “in the absence of corruption, lack of qualifications, or unusual ideological extremism, Democratic presidents have always been allowed to pick liberal justices, and Republican presidents conservative ones.” The first two exceptions are an oblique reference to the allegations against Clarence Thomas, the third to the case against Robert Bork. For the sake of the argument, set those aside. What of Roberts and Alito? Since no one accused either or being corrupt or unqualified, the only remaining justification for all those Democratic votes to keep them off the Court would be that they were extremists. If we accept that characterization, however, it becomes impossible to see how a Republican president could nominate any recognizably Republican jurist to whom Democratic senators would acquiesce.

Seen in this context, Lugar’s votes to confirm Sotomayor and Kagan were instances of unilateral disarmament, upholding a social norm Democrats had jettisoned long ago. Indiana’s Republicans decided they could do better than a senator who agreed with Chait that good Republicans play nice while good Democrats play to win.